Voltage determining arrangement for dielectric heaters



May 22, 1956 c. E. ELLSWORTH VOLTAGE DETERMINING ARRANGEMENT FOR DIELECTRIC HEATERS 2 Sheets-Sheet l Filed Aug. l5, 1953 May 22, 1956 c. E. E| swoRTH 2,747,067

VOLTAGE DETERMINING ARRANGEMENT FOR DIELECTRIC HEATERS Filed Aug. 13, 1955 2 Sheets-5h66?. 2

Fig. 4

nited States Patent O VLTAGE DETERMINING ARRANGEMENT FOR DELECTRIC HEATERS Carl E. Ellsworth, Anchorage, Ky., assignor to National Cylinder Gas Company, Chicago, 111., a corporation of Delaware Application August 13, 1953, Serial No. 374,083

3 Claims. (Cl. 219-10.55)

This invention relates to high-frequency dielectric heating applicators and more particularly to an applicator having integrally included therein at least a portion of an arrangement for measuring the magnitude of the highfrequency potential diterence between heating electrodes of the applicator.

in high-frequency heating, the high potential dierence between the radio-frequency heating electrodes should be known preliminary to and during a heating run. Previous arrangements for such purpose have proven unsatisfactory in one way or another, particularly in applicators having movable or variably spaced electrodes adjustable over a wide range. Such prior systems or devices have required a direct connection to the movable heating electrode with the result the range of electrode movement must be unduly restricted to avoid the Hash-overs occurring when the connection is sufficiently long and flexible to afford a range of electrode movement suitable to meet the differences in work characteristics and operating conditions that are encountered in practice.

in accordance with the present invention, there is provided a voltage determining arrangement which permits unrestricted movement of the heating electrodes without any of the disadvantages present in prior devices. The high-frequency heating electrode itself forms, or has mounted thereon a supplementary capacitive plate which forms, one electrode or plate of a measuring capacitor. The other plate or electrode of the measuring capacitor is mounted on and insulated from a wall of the applicator. More particularly, the supplementary capacitive area is of such size and disposition as to provide for constant capacitance between it and its associated wall mounted plate throughout the range of movement of the heating electrode, if movable. The measuring capacitor may be connected in series with a second impedance of much lower value, preferably another capacitor, which is connected to the other heating electrode so to provide a potential divider. Thus the high-voltage of the heating electrodes may be determined by a voltmeter responsive to the low voltage across the second impedance of the potential divider.

For a more detailed explanation of the invention and for further objects and advantages thereof reference is to be had to the following description, taken in conjunction with the accompanying drawings in which:

Fig. 1 schematically represents a heating applicator embodying the present invention;

Fig. 2 is a sectional view of the measuring capacitor;

Fig. 3 is a front elevation view of the measuring capacitors fixed electrode; and

Fig. 4 is a sectional view of another embodiment of the present invention.

Referring to the drawings, wherein like reference characters designate the same parts throughout the several views and more particularly to Fig. 1, there is shown a high-frequency heating applicator generically similar to the type disclosed in copending Warren application, Serial No. 138,628, tiled January 14, 1950, now aban- 2,747,067 Patented May 22, 1956 Mice doned in favor of Warrens continuation-impart application Serial No. 419,633 tiled March 26, 1954, and comprising an electrically conductive housing 11 having included therein variably spaced heating electrodes 12 and 13 between which a dielectric material to be heated is disposed.

The dielectric material or load may vary in physical dimensions or electrical characteristics thereby requiring adjustment of the applicator. Such adjustment may be effected by changing at least one or more of the various parameters of the applicator such as for example the electrode spacing. The proper settings of these various parameters may be determined from a measure of the potential difference between the heating electrodes. The potential difference between the heating electrodes is determined by a measuring circuit 14 including a measuring capacitor 15 having a fixed electrode or capacitive plate 16 mounted on and insulated from a sidewall of the conductive enclosure 11. The other plate of the measuring capacitor 15 is provided by the upper heating electrode 12 or by a conductive sheet or element 17 mounted on and extending upwardly from the upper heating electrode.

Although, as illustrated the measuring electrode 17 extends wholly upwardly from the heating electrode 12, it will be understood that a portion or all of it may depend below the heating electrode; the only limitation on structure being that it is of such a size so that for all positions of electrode 12 it, together with measuring electrode 113, provides constant capacitance. The potential difference between the heating electrodes, which may be as high as 50 kv. for example, is divided by a potential divider 13 comprised of the measuring capacitor 15 and a variable impedance 19, which is shown to be a capacitor, in series with said measuring capacitor and connected to the lower heating electrode 13. A resistor may replace the cs.- pacitor 19 and for some operating conditions, or when it is desired to employ diiierent forms ot' indicating devices, this may prove advantageous.

In capacitive voltage dividers of the type illustrated, the voltage divides inversely with extent of capacitance in each leg. In carrying out this principle, the capacitance of the variable capacitor 19 is made large with respect to that of the measuring capacitor 15', so as to provide a low voltage for that portion of the measuring circuit 14 exterior to the housing 33. The voltage across the capacitor 19, which is proportional to the potential difference between the heating electrodes 12 and 13, is indicated, in the particular arrangement shown, by an electronic voltmeter including rectifier 2t), capacitor 22, resistors 23 and 24 and ammeter 21. The voltmeter is of the halt' wave peak reading type, as in Zottu Patent No. 2,412,191, and in the particular embodiment illustrated the variousl parameters may, for example, have the following values: resistor 23, 10,000 ohms, resistor 24, 25,000 ohms, capacitor 22, 0.005 microfarad. lt is to be understood that any type of current or voltage measuring device such as an oscillograph, or the like, may be effectively connected across potential-divider impedance 19 in determination of the potential of the heating electrode.

In accordance with the present invention, the supplementary capacitive sheet or skirt 17 of the heating electrode is of such size as to present a constant area to the fixed plate 16, throughout the range of movement of the movable heating electrode 12. During raising or lowering of heating electrode 12, the skirt 17 moves in a path parallel to and adjacent the xed plate 16 so as to maintain a constant distance therebetween, which, together with the constant area presented to the fixed plate or electrode ensures that the capacity of the measuring capacitor 15 remains fixed.

By using the heating electrode skirt, or equivalent, as an element of the measuring capacitor, there is avoided the necessity of providing, as in the aforesaid past practice, a conductor from the movable heating electrode 12 to a separate measuring capacitor. The illustrated structure embodying the present invention permits an unrestricted movement of the heating electrode 12 and avoids flash-over difficulties.

Applicators of the type disclosed include spaced heating electrodes 12 and 13 and inductance structure here illustrated as including an inductor or fin 25 extending from the electrode 12. The housing 11 encloses the inductance structure and the space between the electrodes 12, 13. One end of the iin 25 is electrically connected to the electrode 12 and the other end of the fin is electrically connected to the other electrode 13 by means including wall structure of the housing 11, thus completing a resonant circuit resonant at frequencies predetermined by the inductance structure and the capacitance between the heating electrodes 12, 13. The iin may include pleats 26 or otherwise be made extensible to permit the raising and lowering of the electrode 12. The resonant tank circuit of the applicator is excited by oscillator 27, of the type generically similar to that described and claimed in the aforesaid Warren application Serial No. 419,633, by way of a coupling loop 28 having one end connected to the output of the oscillator and the other end conductively connected to a wall of the housing 11.

As shown, the lower wall of the housing 11 comprises the lower heating electrode 13. However, the lower heating electrode may take the form of an electrically conductive conveyor or platform mounted on and conductively connected with the housing 11. In all cases, the connection from the capacitor 19 to the lower heating electrode 13 is made by Way of the housing 11 which is thereby in circuit with and forms an integral part of the measuring apparatus.

Where the electrodes are fixed or otherwise disposed to contact the load, the electrode voltage may be varied by change in coupling between the oscillator 27 and the load. Such change may be effected by varying the effective loop area in a plane normal to the high-frequency magnetic flux encircling the iin, as for example by means of a shorting bar as taught by the aforesaid Warren apy plications, or by change in the pattern of the electromagnetic field as taught by copending Warren application, Serial No. 419,072, tiled March 26, 1954, as a continuation-in-part of said Warren application, Serial No. 138,628 and as taught by copending Ellsworth application, Serial No. 263,599, tiled December 27, 1951, now U. S. Patent No. 2,712,050.

A preferred mechanical embodiment of the measuring capacitor 1S and its related component parts associated with a double wall applicator is illustrated in Fig. 2. The plate 16 is mounted on an electrically conductive rod 29 within a space or hole in a sidewall 11n of the applicator housing 11 by means of a supporting structure including an insulating plate 30 and metallic spacers 31. The xed capacitive plate 16 is electrically connected to the measz uring circuit by way of a coaxial structure 32 including the electrically conductive rod 29 and coaxial shield 33, and a conductor 34. The rod or inner conductor 29 extends beyond the outer surface of the housing wall 11b and terminates in an electrical connector of any Well known typc exemplied by threaded terminal 35 for receiving a spade 36. The terminal end of the rod 29 is maintained in spaced relation with the coaxial shield 33 by an insulator bushing 37.

The rcctier 20 and its related network of resistors 23, 24 and capacitor 22 arc connected with the terminal 35 by way of the conductor 34, and mounted in close proximity thereto within a metallic housing 4t) which is secured to the outer applicator wall. Due to the highfrequency voltage present the lead 34 and ground lead 34a are made as short as possible in avoidance of excessive inductive reactance. The meter 21 may be mounted on the housing 40 or if desired it may be mounted on a central control panel remote from the instrument housing. In the structure illustrated, there is produced additional capacitance between such components as an iris plate 38 and the fixed measuring capacitive plate 16; the conductive rod 29 and its coaxial shield 33; and the back surface of fixed plate 16 and the shield 33. This additional capacitance is schematically illustrated by dotted lines in Fig. l as being the capacitors 19a and 19b which are effectively in parallel with the variable capacitor 19.

The effective capacitance of the measuring capacitor 15 may be selected or varied by the iris structure 38 which regulates the extent of exposure of the xed electrode plate 16 to the electric field of the applicator. The iris structure is comprised of a metallic plate conductively mounted, in any suitable manner, on the wall 11a of housing 11 intermediate the measuring electrodes 16, 17 and is provided with an aperture 38a formed in the center portion thereof. The plate or electrode 16 and the iris structure 38 are insulated one from the other by a sheet of insulating material 39. The ratio in which the potential difference between the heating electrodes is divided between capacitors 15 and 19 may be approximately determined by varying the size of the aperture 38a of the iris structure 38 to suit a particular applicator or its intended use. This variation may be effected by substituting iris plates having diierent sized apertures or providing an iris structure of the type common to the camera art thereby permitting an infinite number of variations in the size of the opening 38a. The ratio is precisely adjusted by the Calibrating condenser 19.

Another embodiment of the present invention is illustrated in Fig. 4 wherein the voltage determining circuit including the plate 16 is shown associated with a single Wall applicator. The plate 16 is mounted parallel with the direction of movement of the electrode skirt 17, by means of a threaded shaft 29a secured to the insulating plate 30. With this type of construction the capacitance of the various component parts effectively in parallel with the adjustable capacitor 19 is reduced to a minimum, and where as illustrated, the aperture 38a of the iris structure 38 is set for a maximum, the capacitance of the aforesaid parts is of such small value as to be disregarded, i. e., the stray capacities 19a, 19b (Fig. l) are negligibly small. The capacitance of capacitor 15 may be varied for calibration purposes by movement of the plate 16 toward and away from the skirt 17 as by adjustment of the internally threaded members which mount the threaded shaft 29a to the insulated plate 30. It is to be understood, additionally, that the plate 16, Fig. 2, may also be made adjustable toward and away from the skirt 17 and that the manner of eiecting this adjustment is immaterial, and further that the iris structure 38 (Fig. 4) may take that form described in the embodiment of Fig. 2, wherein the iris structure 38 may be of the type having a continuously adjustable aperture 38a.

It is to be understood that the mechanical structure described above is exemplary of the present invention which comprehends modications thereof within the scope of the appended claims.

What is claimed is:

1. In a dielectric heating applicator having spaced heating electrodes, one of which is movable for variation in the spacing between the electrodes, and having means for developing between said electrodes a high-frequency, high-voltage electric eld, the combination of a highfrequency, high-voltage measuring arrangement for determining the voltage between said heating electrodes comprising a first plate movable with said one of said heating lelectrodes as a unit and having a planar surface of large area extending in a direction parallel to the direction of vmovement of said one electrode, a normally stationary second plate having a planar surface extending in opposed parallel spaced relation to said planar surface of said vfirst plate, said tirst and second plates comprising a capacitive measuring impedance, the area of said planar surface of said rst plate being suiciently greater than that of said second plate so that for ail positions of said one electrode said first plate has an area opposite said second plate which is equal to the area of said second plate, whereby the capacitance of said measuring impedance is maintained constant throughout the range of movement of said one of said heating electrodes, a voltage divider comprised of said measuring impedance and a second impedance electrically connected with the other of said heating electrodes, and voltage responsive means in circuit with said second impedance to respond to its voltage as a measure of the voltage between said heating electrodes.

2. In a dielectric heating applicator having spaced heating electrodes, one of which is movable in a direction toward and away from the other electrode for variation in the spacing between the electrodes, and having means for developing between said electrodes a high-frequency, high-voltage electric field, the combination of a high-frequency, high-voltage measuring arrangement for determining the voltage between said heating electrodes comprising a normally stationary plate having a planar surface extending in a direction parallel to said direction of movement of said one electrode, a second plate movable with said one electrode as a unit and having a planar surface of large area extending in a direction parallel to said direction of movement of said one electrode and also extending in opposed parallel spaced relation to said planar surface of said stationary plate, said stationary plate and said second plate comprising a capacitive measuring impedance, the area of said planar surface of said movable second plate being suciently greater than that of said stationary plate so that for all positions of said one electrode said second plate has an area opposite said stationary plate which is equal to the area of said stationary plate, whereby the capacitance of laid measuring impedance is maintained constant throughout the range of movement of said one electrode, a voltage divider comprised of said measuring impedance and a second capacitive impedance electrically connected with said other heating electrode, and voltage responsive means in circuit with said second impedance to respond to its voltage as a measure of the voltage between said heating electrodes.

3. The arrangement as in claim 2, wherein the said heating electrodes are disposed within a conductive walled enclosure, one of the walls of which has an opening disposed in opposed relation to said movable second plate, and wherein said stationary plate is insulated from and supported by said one wall in position to be exposed to said second plate through said opening.

References Cited in the le of this patent UNITED STATES PATENTS 1,580,621 Mahien Apr. 3, 1926 2,309,560 Weltz Jan. 26, 1943 2,412,191 Zottu Dec. 3, 1946 2,438,477 Dodds et al. Mar. 23, 1948 2,467,782 Schuman Apr. 19, 1949 2,504,109 Dakin Apr. 18, 1950 2,522,487 Warren Sept. 12, 1950 2,638,529 Gard May 12, 1953 FOREIGN PATENTS 556,292 Great Britain Sept. 28, 1943 

